Solar collector with integral drain back reservoir

ABSTRACT

The Sol-Reliant solar thermal collector with integral drain back reservoir (USPTO trademark Ser. No. 78,369,183) is the first solar water heater to combine solar collector, drain back reservoir, and photovoltaic module into one complete unit. The drain back system has proven to be the most reliable of all solar water heaters with only one drawback: the size of the pump needed to lift fluid from a remote reservoir. Sol-Reliant overcomes that obstacle by 1) orienting the solar collector horizontally, 2) Placing the reservoir just below the bottom of the solar collector, and 3) integrating a photovoltaic module capable of powering a 12-volt DC pump.

I hereby claim the benefits of the priority of Provisional Application No. 60/559,301 filed Apr. 05, 2004 by John Hugh Patterson.

The Sol-Reliant solar thermal collector (USPTO trademark Ser. No. 78,369,183) is used in domestic hot water heating systems. It consists of a copper absorber plate inside a glazed, insulated box. This is typical construction for most solar thermal flat plate collectors. The Sol-Reliant combines a second element, the drain back reservoir, which in all previous applications has been separate and remote from the collector. In my invention, a large diameter reservoir pipe installed on the return line of the solar collector is located immediately on the underside of the collector just outside the heated box. The purpose of the reservoir is to keep the solar loop-circulating pump primed. When the pump is turned “on”, the fluid in the reservoir is pumped up into the collector where it is heated and then delivered to it's load, which in most cases is a water storage tank. When the pump shuts “off”, the fluid in the collector box drains back by gravity into the reservoir leaving the collector empty. When the fluid drains back into the reservoir, air rises to fill the collector.

An important feature between the collector and the reservoir is the anti-siphoning assembly. This consists of copper and brass reducing fittings which make the transition between the 1½″ reservoir pipe size to the ¾″ or 1″ collector header pipe. This reduction must occur in the vertical plane rather than the horizontal as the piping transitions in size through the collector box. From the reservoir pipe, a 1½″×1″ reducing 90 degree fitting is brazed with the 1½″ side on the horizontal reservoir pipe. The 1″ side of the elbow faces up, perpendicular with the back of the collector. Into the 1″ elbow another elbow oriented 90 degrees from the horizontal reservoir is brazed and faced toward the return header coming from the top of the collector.

The reservoir pipe is enclosed in an insulated chamber to protect against heat losses, and to further protect against the very high temperatures of the thermal collector box just above. During stagnation, when the pump is off and the sun still present, temperatures inside the collector can reach over 400 degrees F.

In building the Sol-Reliant collector with integral reservoir, the collector box must first be built and insulated with high temperature insulation. The copper absorber plate is placed inside. From the underside, in the chosen corner of the collector where the reservoir pipe will connect, a hole is drilled through the back of the collector. The brazed anti-siphoning assembly is attached to the reservoir pipe and fed through this opening.

Thus in a single unit, both the collector and reservoir can be installed. It is important that the collector be installed in a level manner, or very slightly pitched so the reservoir can drain toward the piping serving the solar hot water tank.

BACKGROUND OF THE INVENTION

The Sol-Reliant solar thermal collector (USPTO trademark Ser. No. 78,369,183) is a unique and significant innovation to the traditional drain back system. A closed loop system, the drain back relies on gravity to keep the solar collector empty when freezing or overheating conditions arise. In all other solar water heating systems, freezing and overheating are problems that have to be dealt with; and the drain back system does it best.

Even so, traditional drain back systems had one significant limitation: the reservoir tank was usually located 15 to 30 feet below the top of the solar collector. A rather large pump had to be used to lift the water from the reservoir tank to the top of the solar collector. The parasitic energy loss from operating a high-head pump capable of lifting the water to this height could use 5 to 10% of the equivalent energy saved. Thus there was a need to find a way to lower the vertical head for the pump so less of the system energy was used for pumping. Placing the reservoir as high as possible in the system helps, but placing it directly below the collector, and combing it with the collector in an integral unit proves the best of all possible solutions. The Sol-Reliant does this.

Furthermore, there has been a trend in recent years for active solar energy systems to use pumps powered by photovoltaic (solar electric) modules. Pressurized closed loop glycol systems use small photovoltaic modules to power low head pumps. However, to power a traditional drain back system with a photovoltaic module would take a very large, very expensive module, powering a large, expensive DC pump. By combining solar thermal collector with an integral drain back reservoir located just below the thermal collector, the drain back system pump can be powered by a relatively small photovoltaic module and a low head DC pump.

SUMMARY OF THE INVENTION

The Sol-Reliant solar thermal collector (USPTO trademark Ser. No. 78,369,183) combines a horizontally oriented and mounted solar collector with an integral drain back reservoir. When placed on a rooftop or other structure, this configuration makes for the lowest possible vertical head required for a drain-back system pump to overcome. Furthermore, it makes for a much simpler installation by combining two principal system components into one.

It relieves the need for a high-head pump required in all other drain-back systems thus reducing the parasitic energy losses. It allows the use of relatively inexpensive photovoltaic modules of 40 watts or less to directly power low-head 12-volt DC pumps.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Page 1: Top view of solar panel; FIG. 1.A-without glass; FIG. 1.B-with glass

Page 2: FIG. 2.A-Plumbing diagram; FIG. 2.B-bottom view

Page 3: FIG. 3.A-Location of reservoir on collector; FIG. 3.B-Blow up of anti-siphoning assembly

Page 4: FIG. 4.A-Corner detail of collector box; FIG. 4.B-Location of reservoir beneath collector

Page 5: Cross section of solar collector

Page 6: FIG. 6.A-Detail of reservoir transition to collector box via anti-siphoning assembly FIG. 6.B-Opposite end of reservoir where fluid supply lines fall to solar water storage tank

Page 7: FIG. 7.A-Brackets showing roof clearances for reservoir; FIG. 7.B-Reservoir fluid level

Page 8: Through the roof detail showing final plumbing from collector and roof flashing

DETAILED DESCRIPTION OF THE INVENTION

The Sol-Reliant solar thermal collector (USPTO trademark Ser. No. 78,369,183) features a built in drain back reservoir. All drain back solar water heating systems previously contained a separate drain back reservoir, typically located on top of or near the solar water storage tank below. The drain back solar water heating system relies on gravity and the principal of water and fluids seeking their own level.

The purpose of the reservoir is to keep the circulating pump primed in order to circulate fluid through the solar thermal collector when the pump is “on”. When the pump shuts off, the fluid drains back from the collector into the reservoir leaving the collector empty. It is important in a drain back system both for freezing and for overheating that the collector be empty when the pump is “off”. The reservoir must be large enough in volume to hold the amount of fluid displaced in the solar collector itself and the pipes between the solar collector and the reservoir.

This invention puts the solar collector and the reservoir into one complete unit. Please notice in the enclosed drawings that the reservoir is not a tank, but a long, large diameter pipe, which lies just below the bottom of the collector. The system is charged with a heat transfer fluid (distilled water in non-freezing climates and or anti-freeze fluid in cold climates). When the pump is at rest the fluid level is just below the collector, isolated from the intense heat that can result in a stagnant solar collector (350-400 degrees F.).

Another important feature is the anti-siphoning assembly, which precludes thermal siphoning between a cold solar rooftop collector at night and a heated solar water storage tank below. By transitioning from 1½″ horizontal pipe (the reservoir) to the vertical ¾″ or 1″ solar return line pipe, the elements for siphoning are eliminated. 

1) the sol-reliant solar thermal collector with integral drain back reservoir USPTO trademark Ser. No. 78,369,183) is the first solar water heater to combine solar collector and drain back reservoir into one complete unit. 2) The Sol-Reliant also includes an integral photovoltaic module capable of powering a 12-volt DC circulating pump for the drain-back system. 3) The Sol-Reliant system contains 3 distinct components: the solar thermal collector, the drain-back reservoir, and the photovoltaic module assembled together as an integrated and complete unit, capable of powering a 12-volt DC circulating pump. 